U.S. Patent Application, U.S. Pat. No. 4,523,226 filed Jan. 19, 1983 describes a stereoscopic video system which utilizes a standard television field of 262.5 lines but which has two subfields in an "over-and-under" format, one above and the other below, each having 131.25 lines. Each subfield contains an image with the appropriate left or right perspective view. When displayed on a normal 60 Hz monitor the images are anamorphically compressed by a factor of two in the vertical direction, because half the number of lines is scanned for each subfield compared to that which is scanned in a normal field. However, when played back on a 120 Hz monitor, 120 fields per second are displayed, each field having 131.25 lines. Accordingly, when viewing the image through the appropriate selection device, each eye sees 60 fields per second. Since the number of fields per second is above the critical fusion frequency, flicker, which has been evident in prior art systems, is not present.
To accomplish this, left and right cameras which are modified to run at 120 Hz are utilized. When used with the appropriate switching electronics, the cameras produce the "over-and-under" format of 131.25 lines above, and 131.25 lines below. Cameras which produce 120 fields per second are uncommon and, generally speaking, not provided by manufacturers. In order to produce the needed left-right-left-right sequence of fields in one stereoscopic frame within one thirtieth of a second, for a flickerless image, cameras need to be modified for a field rate higher than the usual 60 Hz. This modification is generally simpler for black and white than color cameras, since certain color cameras, especially those with a single tube, are difficult to operate at 120 Hz while producing a good color signal. Such modifications entail the significant expense of conversion and calibration.